Hi am Vishnu Tejas. i would like to get details on optical communication and networking book by gayathri pdf ..I am a 7th sem ECe student of Anna university and I am preparing for examinations scheduled in November.

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Hi am Vishnu Tejas. i would like to get details on optical communication and networking book by gayathri pdf ..I am a 7th sem ECe student of Anna university and I am preparing for examinations scheduled in November.

1. Define a fiber optic system.
Fiber optic system consists of a fiber optic cable, a light source and a light detector. The
optic fiber is used to carry the light beam from one place to another.
2. What are the uses of optical fibers?
a) To transmit the information of telephone communication, computer data, etc.
which are in the form of coded light signals
b) To transmit the optical images (Example : Endoscopy)
c) To act as a light source at the inaccessible places.
d) To act as sensors to do mechanical, electrical and magnetic measurements.
3. Differentiate between glass and plastic fiber cables.
Fiber optic cables are made from glass and fiber. Glass has the lowest loss but it is brittle.
Plastic is cheaper and more flexible but has high attenuation.
4. Mention the advantages of optical fiber communication.
1. Large information capacity 2. Long distance transmission
3. Small size and low weight 4. Electrical isolation
5. Immunity to crosstalk and EMI 6. Increased signal security
7. Enhanced safety 8. Ruggedness and flexibility
9. System reliability and easy maintenance 10. Low cost
5. Define reflection.
The law of reflection states that the angle at which the ray strikes the interface is exactly
equal to the angle that the reflected ray makes with the imaginary perpendicular normal.
6. Define refraction.
Refraction occurs when light ray passes from one medium to another i.e. the light ray
changes direction at the interface. The refraction (bending) takes place because light travels at
different speed in different mediums.
7. What is Snell’s law?
Snell’s law states how light ray reacts when it meets the interface of two mediums having
different refractive indices. Hence it is the relationship at the interface of two mediums and is
given by
n1sinΦ1=n2 sinΦ2.
where n1 is the refractive index of medium 1
n2 is the refractive index of medium 2
Φ1 is the angle of incidence
Φ2 is the angle of refraction
EC2402 – OPTICAL COMMUNICATION AND NETWORKS
AMSEC/ECE Prepared By : Mr.A.Natarajan, ASP/ECE
8. What is total internal reflection?
When the incidence angle is increased beyond the critical angle, the light ray does not pass
through the interface into the other medium. This gives the effect of mirror existing at the interface
with no possibility of light escaping outside the medium. In this, the angle of reflection is equal to
the angle of incidence. This action is called the total internal reflection of the beam.
9. What are the conditions for total internal reflection?
a) Light should travel from denser medium to rarer medium.
b) The angle of incidence should be greater than the critical angle of the denser Medium.
10. What is internal reflection?
When the reflection of light is of a less optically dense material, it is called internal
reflection.
11. What is external reflection?
When light travelling in a certain medium is reflected off an optically denser material it is
referred to as external reflection.
12. What is meant by refractive index of a material?
The amount of refraction or bending that occurs at the interface of two materials of
different densities is expressed as refractive index of two materials. It is the ratio between the
speed of light in air and the speed of light in the material and is given by n = c /v.
13. What is critical angle of incidence?
The critical angle is the angle of incidence that causes the refracted light to travel along the
interface between two different mediums. It is also defined as the minimum angle of incidence at
which the ray strikes the interface of two media and causes an angle of refraction equal to 900
.
Critical angle of incidence Φc= sin-1 (n2 / n1) where n1 is the refractive index of medium1
n2 is the refractive index of medium 2
14. Define acceptance angle. (Nov 14)
The maximum angle ‘Φmax’ with which a ray of light can enter through the entrance end of
the fiber and still be totally internally reflected is called acceptance angle of the fiber.
15. Define acceptance cone.
Rotating the acceptance angle ‘Φmax’ around the fiber axis, a cone shaped pattern is
obtained. It is called the acceptance cone of the fiber input. In other words, the acceptance cone is
the angle within which the light is accepted into the core and is able to travel along the fiber.
16. Write the expression for the refractive index in graded index fibers.
n® =n1[1-2∆(r/a)α
]
1/2for 0 ≤ r ≤ a
= n1(1-2∆)
1/2≈ n1 (1-∆) = n2for r ≥ a
r →radial distance from fiber axis a→ core radius
n1→ refractive index at the core n2→refractive index at the cladding
α →shape of the index profile ∆→ index difference
EC2402 – OPTICAL COMMUNICATION AND NETWORKS
AMSEC/ECE Prepared By : Mr.A.Natarajan, ASP/ECE
17. What is the necessity of cladding for an optical fiber?
a) To provide proper light guidance inside the core
b) To avoid leakage of light from the fiber
c) To provide mechanical strength for the fiber
d) To protect the core from scratches and other mechanical damages
e) To protect the core from absorbing surface contaminants
18. Define relative refractive index difference.
∆ = n1
2 – n
2
2 / 2n1
2 ≈ n1-n2 / n1
Thus relative refractive index difference is the ratio between the refractive index difference (of
core and cladding) and refractive index of core.
19. Define Numerical aperture of a step index fiber. (Nov 14)
Numerical aperture (N.A) of the fiber is the light collecting capability of the fiber and is the
measure of the amount of light rays that can be accepted by the fiber. It is equal to the sine of
acceptance angle.
N.A = sinΦmax = (n1
2
-n2
2
)
1/2 =n1(2∆)
1/2 where n1and n2are the refractive indices of core
and cladding respectively and ∆ is the index difference
20.Give the expression for numerical aperture in graded index fibers.
N.A.®=N.A.(0) [1-(r/a) α
]
1/2 for r≤ a
Where N.A(0) = axial numerical aperture = (n1
2
-n2
2
)
1/2
a is core radius and
α is the refractive index profile.
21. What is an index profile?
The index profile of an optical fiber is a graphical representation of the magnitude of the
refractive index across the fiber.
22. Define Mode-field diameter.
The mode-field diameter (MFD) is the fundamental parameter of a single mode fiber. This
can be determined from the mode field distribution of the fundamental LP01 mode.
23. Why do we prefer step index single mode fiber for long distance communication? Or List
the advantages of single mode fibers. (Nov 14)
Step index single mode fiber has
a) low attenuation due to smaller core diameter
b) higher bandwidth and
c) very low dispersion.
24. What is tunnel effect?
The leaky modes are continuously radiating their power out of the core as they propagate
along the fiber. This power radiation out of the waveguide due to a quantum mechanical
phenomenon is known as the tunnel effect.
EC2402 – OPTICAL COMMUNICATION AND NETWORKS
AMSEC/ECE Prepared By : Mr.A.Natarajan, ASP/ECE
25. What is the principle used in the working of fibers as light guides?
The phenomenon of total internal reflection is used to guide the light in the optical fiber. To
get total internal reflection, the ray should travel from denser to rarer i.e. from core to clad region
of the fiber and the angle of incidence in the denser medium should be greater than the critical
angle of that medium.
26. What are step index and graded index fibers?
If the refractive index of the core in a fiber is uniform throughout and undergoes abrupt
change (or step) at the cladding boundary, it is called step index fiber. The light propagation is
mainly by meridional rays.
If the refractive index of the core in a fiber is made to vary as a function of the radial
distance from the centre of the fiber, it is called graded index fiber, i.e. the refractive index
decreases as the radial distance increases. Here the light propagation is by skew rays.
27. What are leaky modes in optical fibers?
Leaky modes are the modes that are partially confined to the core region and attenuate
continuously by radiating their power out of the core as they propagate along the fiber.
28. What is V number or normalized frequency of fiber? (Nov 2014)
V number of fiber or normalized frequency of fiber is used to find the number of
propagating modes through the fiber. V = 2πa (N.A) / λ
In step index fiber number of modes propagating through the fiber=V
2
/2.
Taking the two possible polarizations, total number of possible modes propagating through the
fiber = V
2 / 2 *2 = V2.
29. What are meridional rays?
Meridional rays are the rays which follow the Zig Zag path when they travel through fiber
and for every reflection they will cross the fiber axis.
30. What are skew rays?
Skew rays are the rays which follow the helical path around the fiber axis when they travel
through the fiber and they would not cross the fiber axis at any time.
31. What is fiber birefringence?
Fiber imperfections such as asymmetrical lateral stress, non circular imperfect variations of
refractive index profile break the circular symmetry of ideal fiber and modes propagate with
different phase velocity and the difference between their refractive index is called fiber
birefringence. B=ko(ny-nx)
32. Define phase velocity.
For plane waves, the constant phase points form a surface called wave front. As a
monochromatic light wave propagates along a waveguide in the z direction these points of
constant phase travel at a phase velocity vp given by vp= ω/β, where ω is the angular frequency of
the wave and β is the wave propagation constant.
EC2402 – OPTICAL COMMUNICATION AND NETWORKS
AMSEC/ECE Prepared By : Mr.A.Natarajan, ASP/ECE
33. Define group velocity.
The light energy is composed of a sum of plane wave components of different frequencies.
When a group of waves with closely similar frequencies propagate, their resultant forms a packet
of waves. This wave packet does not travel at the phase velocity of the individual waves but
moves at a group velocity vg = δω/δβ.
34. What is a wave front?
Within all electromagnetic waves, there are points of constant phase. For plane waves these
constant phase points form a surface called wave front.
35. Define wavelength.
Wavelength is the distance travelled by one cycle of an electromagnetic wave.
Wavelength (λ) = c/f = speed of light in air / frequency
UNIT- II - TRANSMISSION CHARACTERISTICS OF
OPTICAL FIBERS
1. Mention the losses responsible for attenuation in optical fibers.
Absorption losses, scattering losses and radiative losses
2. Define fiber loss or signal attenuation.
Attenuation is a measure of decay of signal strength or loss of light power that occurs as
light pulses propagate through the length of the fiber. It helps to determine the maximum
transmission distance between a transmitter and a receiver.
3. What are the three different mechanisms which cause absorption?
1. Absorption by atomic defects in the glass composition
2. Extrinsic absorption by impurity atoms in the glass material
3. Intrinsic absorption by the basic constituent atoms of the fiber material.
4. What do you mean by extrinsic absorption?
Absorption phenomena due to impurity atoms present in the fiber.
5. Mention the factors that cause Scattering losses.
Scattering losses in glasses arise from
1. Microscopic variations in the material density
2. Compositional fluctuations
3. Structural inhomogeneities (or) defects occurring during fiber manufacture.
6. What are the types of scattering losses?
a) Linear scattering loss 1. Rayleigh scattering 2. Mie scattering
b) Non-Linear scattering 1. Stimulated Brillouin scattering
2. Stimulated Raman scattering
EC2402 – OPTICAL COMMUNICATION AND NETWORKS
AMSEC/ECE Prepared By : Mr.A.Natarajan, ASP/ECE
7. What is Rayleigh scattering?
Due to Microscopic variations in the material density and compositional fluctuations, there
will be refractive index variations within the glass. This index variation causes a Rayleigh type of
scattering of light. Rayleigh scattering in glass is the same phenomenon that scatters light from
sun in the atmosphere, giving rise to a blue sky.
The expression for Rayleigh scattering loss is given by
αscat=(8π3
/3λ2
)(n2
-1)2kBTfβT λ=operative wavelength
n=refractive index kB= Boltzmann’s constant
βT= isothermal compressibility Tf=fictive temperature
8. Define macroscopic bending losses.
Macroscopic bending occurs when the radius of curvature of bend is greater than the fiber
diameter. As the radius of curvature of bend decreases, the loss increases exponentially until at a
certain critical radius, the curvature loss becomes observable.
9. Define microscopic bending.
Micro bends are repetitive small- scale fluctuations in the radius of curvature of the fiber
axis. They are caused either by non-uniformities in the manufacturing of the fiber or by nonuniform
lateral pressures created during the cabling of the fiber.
10. Define cutoff wavelength of the fiber.
The cutoff wavelength is defined as the minimum value of wavelength that can be
transmitted through the fiber. i.e. The light with wavelengths greater than the cutoff wavelengths
can be transmitted. λcutoff = 2πa (N.A) / V
11. What is Mode Coupling?
The waveguide non uniformities such as deviations of the fiber axis from straightness,
variations in the core diameter, irregularities at the core-cladding interface and refractive index
variations may change the propagation characteristics of the fiber. This produces the effect of
coupling energy from one mode to another which is called as mode coupling.